Turbine Performance Monitoring
Turbine Performance Monitoring
Turbine Performance Monitoring
By
M.S. & R.H. Steam Temperatures M.S. Steam Pressure Condenser Vacuum Final Feed Water Temperature DP Across Feed Regulation Station Auxiliary Power Consumption Make Up Water Consumption
Cycle Efficiency is reduced by 1% with fall of inlet steam parameters as below: Temperature @400C Pressure @25Kg/cm2 Steam leakages from Main Steam line results into heat loss @3050-3260 KJ per Kg of steam or: 1% Main Steam Loss = 1.15% Heat Loss 1% Soot Blowing = 0.8% Heat Loss
1%Condensate Loss = 0.1% Heat Loss 1% Feed Water Loss After Final Heater = 0.4% Heat Loss 1% Blow Down = 0.25 - 0.5% Heat Loss
It is a misconception that minimum back pressure should be maintained at all loads However,this is not true. The lower back pressure is justified only if the efficiency gain due to this is greater than power consumption of CW pumps & cooling tower fans
Silica deposition causes the passage areas between blades to progressively reduce Increases the first stage pressure of turbine progressively The Cylinder efficiency is reduced
Do not raise the boiler pressure until Silica level is normal Give Blow down as required Minimum use of superheater & reheater spray Steam washing of turbine by wet steam at low speeds
Feed heaters survey evaluate the performance of heaters & predicts the deterioration causes Following parameters are noted down - Steam pressure at heater - Steam temperature at heater - Feed water inlet & outlet temperature - Heater drain temperature
In throttle governed machine ,the load is directly proportional to first stage pr. In constant pr. Operation load reduction is achieved by throttling the steam flow through control valves Throttling increases the Entropy & reduces temperature & available energy in the steam The exhaust steam wetness is reduced Net effect is to reduce the cycle efficiency
In sliding pressure operation,the control valves are kept wide open & the pressure before the stop valves is varied through boiler to achieve required part load This reduces throttling losses across control valves The initial temperature is maintained at reduced pressure unlike throttling process The net effect is to improve cycle efficiency as compared to constant pressure operation
Always maintain MS & RH temperatures at 540+50C Maintain rated MS pressure of 150 Kg/cm2 Adopt sliding pressure operation at part loads While loading the set check that IP control valves are full open after approx. 20% load Check that HP-LP bypass valves are closed Put LP & HP heaters in service at appropriate time Avoid Reheater spray
Water will leak from a given size opening at a greater rate than steam as shown in table Notice that doubling the size of the hole increases the loss by four times
Maloperation/Passing of Valves
Passing of water or steam to drains to waste due to leakage of drain valves, steam traps,safety valves on the piping All the steam line drain valves of turbine side should be closed immediately after rolling Check that MAL drain valves of turbine system close on temperature criteria Close warm-up valves of HP-LP bypass after charging
Maloperation/Passing of Valves
Close all vents of condensate line ,feed water line, heaters after charging Check that bypass valves of main control lines are closed Check the orifices of Deaerator vent,BFP balancing leak-off for erosion ,replace them if necessary
In old power stations aux.power consumption used to be >11%, which has been now reduced to 7-8% by dispensing of some pumps,providing efficient auxiliaries etc However, the reasons for higher works power are: - Partial loading of generating unit - Keeping more auxiliaries in service,or at higher load than needed - Poor condition of equipments
Measures to be Taken
At loads lower than 60% Switch off one auxiliary & load the running one fully CW pumps should be operated only in accordance with optimisation curve so that benefit achieved from running the pump is greater than the cost of running it The power consumption of variable speed drives varies as the cube of the speed Doubling the power requires eight times power
Whenever a variable speed pump or fan is in service it should be operated at minimum possible speed that will do the job During parallel operation of both the equipments should be loaded equally In case of BFP keep watch on Balancing Leak off pressure & thrust bearing temp. Check that recirculation valve closes at 220 t/hr
Working oil temp. less than 900C at rated load Strainer DP should be less than 0.5 Kg/cm2 Never overload BFP otherwise Cavitation will be promoted due to deterioration of NPSH at high flows Always maintain the DP across the Feed Regulation Station about 5-6 Kg/cm2. Higher DP will increase throttling losses
Prevent sudden changes in steam parameters,particularly temperatures Never cross the temperature limits Low steam temperature leads to cooling of rotor resulting negative diff. Expansion & chances of condensation in last stages Strictly follow startup curves/ criteria curves during unit start-up Never bypass the TSE influence & do not violate TSE temperature/load margins
Do not cut-short soaking time during turbine start-up,otherwise this will lead to lower load margins later Ensure closure of all MAL drain valves as per temperature criteria.Close steam line drain valves after rolling Do not hold the turbine below block load (10%) Maintain lube oil inlet temperature between 42450C Establish feed heaters as soon as NRV releases are available
Normally avoid use of CRH spray for reheater temperature control Ensure regular cleaning of CW system strainers Try to reduce make-up water consumption (normal 3%) by checking water & steam leakages in the system Change over the auxiliaries time to time to maintain their running hours Perform ATT once in a fortnight